those of you who have used Tyvek for a MYOG bivy or other shelter,how breatheable have you found Tyvek to be ?how do the condensation issues compare to other single wall fabrics ?is it truly waterproof and breatheable ?

I've had better luck on breathability with the "clothes" version of Tyvek(1443r) versus the homewrap version(1085d). The homewrap is breathable, although very little when compared to fabrics like eVent. Have found it to be very waterproof.

Definitely recommend 1443R over Homewrap. The specs are on the internet somewhere if you dig for them (maybe on Dupont's website?), and I remember 1443R having a much higher MVTR. It's still pretty low though- if I remember correctly it's less breathable than PU coatings. I experienced moderate condensation in my Tyvek bivy. It is VERY warm - much warmer than something like a MLD Superlight bivy. It kept my bag totally dry in a wet snow storm when my soaked tarp sagged in on me all night.

The 1443R should be strong enough for a single wall tent. The material itself is quite strong and has some ripstop behavior. I recommend using the Tyvek tape- I cut it in half so it was 1" wide and applied a 1" strip to each side of the seam. This type of seam is both waterproof and stronger than the fabric. I recommend avoiding stitching whenever possible- it greatly weakens the fabric. If you do have to stitch any seams, use a long stitch then cover with Tyvek tape afterwards.

Andrew

P.S. I don't have much use for a bivy so I have been half-heartedly trying to sell mine for awhile. Let me know if you are interested.

Should work for tent shelter although my tyvek bivy is extremely warm and is not extremely breathable.I use the indoor/outdoor double sided carpet tape with fiber reinforcement.it is 2" but I cut it in narrow strips.Rub it down flat and let sit 24 hours. The tyvek will fail before the seam.

I have also sprayed the Tyvek with DWR to augment the water proofness.

Depends on the tent material. If it is uncoated nylon with or without DWR the nylon will be more breathable. If it is waterproof nylon or silnylon the Tyvek might be more breathable. Note I am not aware of any thens made with waterproof breathable Nylon. The waterproof coating on most nylons is none braethable polyurethane while most rain jackets are breathable polyurethane.

I recently looked for the MVTR for Tyvek 1443R and found the box in the chart I found on the Dupont website didn't list any number. For Tyvek 1460R (a stronger, slightly heavier version 1443R with greater hydrostatic head rating) was listed at greater than 800. 800 is below the rating of most breathable rain jackets.

"do you think the homewrap version is breatheable enough for a small single wall tent ?"

Certainly if you have enough venting. Awhile back, i made a modified tube tent out of homewrap, and it worked fairly well except when it was very humid. But there wasn't enough venting. Keep in mind though, homewrap packs rather bulky, and a tent is going to be especially big and bulky. A mid sized tarp would be better.

"is the clothes version strong enough for a single wall tent ?"

In my opinion no, which is unfortunate because i really like the "Kite" (or "clothes") tyvek material for it's breathability, smaller packing, less slippery, and lower weight over the homewrap. I made a double bivy out of it, and my wife didn't take any care and would sit up abruptly not paying attention to straining the material, and after only a couple of times it has started to rip and fray (i've since converted into two single bivies). Homewrap is much tougher and strong.

Plus the lighter, more breathable stuff, it's not near water resistant enough to use in a tent unless you plan to never take it out in rain. (Home wrap is though)

I made a bivy out of the kite stuff (1443r) and am very happy with it. Waterproof enough. I'll echo though, that it is more warm than breathable, which works okay for me- it is my winter bivy.I haven't had condensation issues, but it is certainly not as breathable as something like goretex or event or fancy stuff.